1. Field of the Invention
The present invention relates to a switching valve device used for vacuum suction of a member such as a semiconductor chip.
2. Description of the Related Art
Conventionally, in a semiconductor manufacturing field, devices such as a mounter and a handler are used a lot for assembly, transfer, and so on of a member such as a semiconductor chip.
The devices such as the mounter and the handler transfers a product such as the semiconductor chip accurately to a predetermined position of a predetermined processing machine or measuring machine. Vacuum suction is used frequently for holding the product.
FIG. 31 shows a switching valve device used for such vacuum suction, and this switching valve device includes a vacuum suction switching valve 1 and a vacuum break switching valve 3.
The vacuum suction switching valve 1 is composed of a 2-port/2-position electromagnetic switching valve and a vacuum port V is connected to a vacuum source not shown.
The vacuum break switching valve 3 is composed of a 2-port/2-position electromagnetic switching valve and a pressurization port P is connected to a pressurization source not shown.
In such a switching valve device, for example, by turning on a solenoid 5 (hereinafter referred to as a vacuum solenoid) of the vacuum suction switching valve 1 in the handler, the product is attached by suction to a vacuum suction unit not shown connected to an output port A.
When the product is then transferred to a predetermined position for detachment, the vacuum solenoid 5 is turned off, and a solenoid 7 (hereinafter referred to as a vacuum break solenoid) of the vacuum break switching valve 3 is turned on.
Consequently, pressure air is supplied from the pressurization port P of the vacuum break switching valve 3, and the product is detached without fail from the vacuum suction unit connected to the output port A.
However, in such a switching valve device, there is a problem that at the turning-on of the vacuum break solenoid 7, sudden supply of the pressure air from the pressurization port P of the vacuum break switching valve 3 through the output port A to the vacuum suction unit causes overshoot due to a sudden increase in the internal pressure of a product attaching portion, which makes it difficult to smoothly detach the product attached by suction to the vacuum suction unit.
Namely, the sudden detachment of the product attached by suction to the vacuum suction unit from the product attaching portion may cause a problem that the product is mounted to a position which is displaced from the predetermined position, resulting in a trouble to perform the following work step. This positional displacement exerts an influence even on surrounding products, which may cause further positional displacement of other products.
There is another problem that vacuum suction force, that is, vacuum pressure, varies and its arrival time to the atmospheric pressure and the amount of overshoot change so that it is very difficult to always smoothly detach the product attached by suction to the vacuum suction unit at a set break air flow rate.
FIG. 32 shows a pressure change characteristic in the general usage of the switching valve device shown in FIG. 31. An electrical signal to the vacuum break solenoid 7 is turned on a time t1 after the turning-off of an electrical signal to the vacuum solenoid 5. The electrical signal supplied to the vacuum break solenoid 7 is turned off a time t2 later.
The pressure change during this period is as follows.
The vacuum solenoid 5 is turned off a response delay time T1 after the electrical signal to the vacuum solenoid 5 is turned off, and the supply of vacuum pressure ceases. As a result, held vacuum pressure starts to decrease gradually.
Further, when the time t1 elapses after the electrical signal to the vacuum solenoid 5 is turned off, the electrical signal to the vacuum break solenoid 7 is turned on. When a response delay time T2 elapses after it is turned on, the vacuum break solenoid 7 is turned on, supplying positive pressure as vacuum break pressure. As a result, the pressure in the output port A abruptly increases.
The electrical signal to the vacuum break solenoid 7 is in an on state for the time t2 until the pressure in the output port A approaches the pressure of the atmosphere, and thereafter it is turned off. The vacuum break solenoid 7 is brought into an off state a response delay time T3 after the electrical signal to the vacuum break solenoid 7 is turned off, so that the supply of vacuum break pressure ceases and the pressure in the output port A converges to the atmospheric pressure.
However, such a conventional switching valve device has the following problems.
For example, if the vacuum pressure is set to V, the pressure at a point in time when the vacuum break pressure starts to flow in changes between VL′ and VH′ because the set vacuum pressure drops to VL or conversely rises to VH depending on the amount of the vacuum pressure used.
With a fixed on-period of the vacuum break solenoid 7, when vacuum break starts at the pressure VL′ which is close to the atmospheric pressure, the pressure will overshoot beyond the atmospheric pressure, and throw a workpiece attached by suction and even surrounding workpieces.
Conversely, when vacuum break starts at the pressure VH′, the process of vacuum break is completed before the pressure reaches the atmospheric pressure, and proceeds to the next process without releasing the workpiece.
As a measure against the workpiece being thrown, it is possible to suppress an increase in the pressure in the output port A by shortening the time t2 to cut off the supply of vacuum break pressure earlier. However, in this case, the occurrence of the incident in which the workpiece is not released increases.
Conversely, as a measure against the workpiece being not released, it is possible to reduce the occurrence of the incident in which the workpiece is not released by prolonging the time t2 to cut off the supply of vacuum break pressure later. However, in this case, the occurrence of the incident in which the workpiece is thrown increases.
To solve such problems, there is a conventionally known switching valve device, as shown in FIG. 33, provided with a flow rate adjusting throttle valve 9 on the outlet side of the vacuum break switching valve 3. The pressure change in the general usage of this switching valve device is about the same as that of the switching valve device shown in FIG. 31.
However, this switching valve device adjusts the flow rate adjusting throttle valve 9 provided on the outlet side of the vacuum break switching valve 3 during the pressure change, so that the pressure increases more gently compared to when the throttle valve 9 is not used as shown in FIG. 34, which reduces such an overshoot that the workpiece is thrown at a point in time when the pressure converges to the atmospheric pressure.
The same effect can be obtained even if the vacuum pressure changes to VL or VH from a set vacuum pressure V.
However, in this switching valve device, the pressure increases gently but slowly. This affects the tact time very much in the case of devices such as a mounter for mounting many semiconductor chips on a substrate, which causes a large negative factor affecting device performance.